[sw, dif_aes] Introduce AES unittests

This change introduces a set of AES mock tests to test the public
API. The aim is to validate the API implementation in terms of
different use-cases.

Signed-off-by: Silvestrs Timofejevs <silvestrst@lowrisc.org>

sw/device/tests/dif/dif_aes_test.cc

diff --git a/sw/device/tests/dif/dif_aes_test.cc b/sw/device/tests/dif/dif_aes_test.cc
new file mode 100644
index 0000000..13b1f73
--- /dev/null
+++ b/sw/device/tests/dif/dif_aes_test.cc
@@ -0,0 +1,24 @@
+// Copyright lowRISC contributors.
+// Licensed under the Apache License, Version 2.0, see LICENSE for details.
+// SPDX-License-Identifier: Apache-2.0
+
+#include "sw/device/lib/dif/dif_aes.h"
+
+#include "gtest/gtest.h"
+#include "sw/device/lib/base/mmio.h"
+#include "sw/device/lib/testing/mock_mmio.h"
+
+extern "C" {
+#include "aes_regs.h"  // Generated.
+}  // extern "C"
+
+namespace dif_aes_test {
+namespace {
+using mock_mmio::MmioTest;
+using mock_mmio::MockDevice;
+using testing::Test;
+
+// CODE HERE
+
+}  // namespace
+}  // namespace dif_aes_test

sw/device/tests/dif/meson.build

diff --git a/sw/device/tests/dif/meson.build b/sw/device/tests/dif/meson.build
index 0ca0098..41c0461 100644
--- a/sw/device/tests/dif/meson.build
+++ b/sw/device/tests/dif/meson.build
@@ -194,6 +194,22 @@
   cpp_args: ['-DMOCK_MMIO'],
 ))
 
+test('dif_aes_test', executable(
+  'dif_aes_test',
+  sources: [
+    hw_ip_aes_reg_h,
+    meson.source_root() / 'sw/device/lib/dif/dif_aes.c',
+    'dif_aes_test.cc',
+  ],
+  dependencies: [
+    sw_vendor_gtest,
+    sw_lib_testing_mock_mmio,
+  ],
+  native: true,
+  c_args: ['-DMOCK_MMIO'], 
+  cpp_args: ['-DMOCK_MMIO'],
+))
+
 dif_plic_smoketest_lib = declare_dependency(
   link_with: static_library(
     'dif_plic_smoketest_lib',